```
def numberOfArithmeticSlices(self, A):
if len(A)<3:
return 0
num=0
count=2 #counter. used for calculations
difference=A[1]-A[0] #initialize the difference
for n in range(2,len(A)):
if A[n]-A[n-1]==difference:
count+=1
else:
if count>=3:
num += (count-2)*(count-1)/2 #calculate the nth of 1,3,6,10... use formula nth=n(n-1)/2
count=2 #reset counter
difference=A[n]-A[n-1] #reset difference
if count>=3:
num += (count-2)*(count-1)/2
return num
"""
:type A: List[int]
:rtype: int
"""
```